1. Field of the Invention
The invention relates to the field of Peltier, or thermoelectric coolers and in particular to Peltier coolers using semiconductor materials.
2. Description of the Prior Art
A Peltier cooler is a well known cooling device wherein an electrical current is passed through a series of electrical junctions between unlike materials with high Seebeck coefficients. Because of the change in specific electron entropy when electrons flow across junctions of unlike materials, heat is released in the form of phonons or high frequency lattice vibrations at one junction and absorbed at the opposite junction. As a result of the phonon creation and destruction, one junction heats up while the other is cooled. The number of junctions can be replicated in a serial electrical connection of elements of opposing junctions to increase cooling and heating capacity. The devices may be staged, with one device heat sinked to another, to increase the total temperature differential spanned by the staged series of devices.
However, the cooling capacity of conventional Peltier coolers is dependent upon the integrated electron entropy of the distribution of electrons in the quantum energy levels of the conduction bands in the materials comprising each side of the Peltier junction. This in turn is dependent upon the temperature of the junction. While useful devices may be fabricated from a series of semiconductor-to-semiconductor junctions or metal-to-metal junctions, such prior art Peltier coolers become inefficient at lower temperature, particularly in the cryogenic range below 150 degrees Kelvin.
Therefore, what is needed is a Peltier cooler design which operates efficiently at cryogenic temperature and provides a useful amount of refrigeration.